1. Field of the Invention
The present invention relates to an image forming apparatus which includes a guide member guiding a transfer material to a transfer portion in the image forming apparatus such as a printer, a copying machine, and a facsimile.
2. Related Background Art
A guide member guiding a transfer material (paper or resin film) to which a toner image borne on an image bearing member (photosensitive drum or intermediate transfer belt) is transferred to a transfer portion between the image bearing member and a transfer member is well known.
It is preferable that the transfer material is conveyed along the image bearing member without forming a gap between the image bearing member and the transfer material before the transfer material runs into a transfer electrical field area formed by applying transfer bias to the transfer member. At this point, in the case where there is the gap between the image bearing member and the transfer material, when the toner image is moved from the image bearing member to the transfer material, the toner image flies away or abnormal discharge is generated in the gap, which sometimes results in the generation of the defective image.
Therefore, it is necessary that the transfer material is conveyed along the image bearing member from before running into the transfer electric field area, the guide member has a configuration in which the guide member is close to the image bearing member or the transfer electric field area in order to improve position accuracy at which the transfer material runs into the image bearing member.
However, when the guide member is close to the image bearing member or the transfer electric field area, contamination is easily generated by toner. Namely, the unnecessary toner easily adheres to the transfer material. When the toner adheres to the guide member, a problem that the transfer material guided by the guide member is contaminated by the toner is generated. Further, when the guide member is close to the transfer member, there is also the problem that transfer bias applied to the transfer member leaks to the guide member.
Because of the nature of the guide member, the guide member is strongly slid with the transfer material during a conveying process in which the transfer material is conveyed to the transfer electric field area. Therefore, depending on the configuration of the transfer portion, sometimes the transfer material is frictionally charged by the excessive slide between the transfer material and the guide member. When the transfer material is frictionally charged, since charge on the transfer material disturbs the movement of the toner to the transfer material by the transfer bias, the transfer from the image bearing member to the transfer material does not occur and the toner remains on the image bearing member. As a result, the transfer image appears as the abnormal image. At this point, in the case where the transfer material is in a dry state or in the case where the configuration of the guide member in the image forming apparatus has the strong slide with the transfer material, the abnormal image becomes remarkable.
Namely, the above-described drawbacks are as follows:
(1) the toner contamination of the guide member;
(2) the leakage of the transfer bias to the guide member; and
(3) the charging of the transfer material caused by the slide between the transfer material and the guide member.
In order to prevent the drawbacks, some inventions concerning the guide member have been made.
With reference to (1) the toner contamination of the guide member, there has been made the invention in which potential of the guide member charged by the slide with the transfer material is held in the same polarity as the toner in such a manner that the guide member is formed by a conductive member and the bias having the same electric polarity as the toner is applied or the guide member made of the conductive member is grounded through a varistor, or the invention in which repulsion of the toner is generated in such a manner that the guide member is made of an insulating material and a triboelectric series with the transfer material is caused to be the same polarity as the toner (see Japanese Patent Application Laid-Open No. H07-056451 and Japanese Patent Application Laid-Open No. H11-338276).
With reference to (2) the leakage of the transfer bias to the guide member, there is the invention in which on a structure in which, on the bias having the same polarity as the toner is applied to the inside conductive member, the conductive member is cover with the insulating member and the leakage of the transfer bias is prevented (see Japanese Patent Application Laid-Open No. 10-171258).
With reference to (3) the charging of the transfer material caused by the slide between the transfer material and the guide member, there has been made the invention in which the guide member is grounded to remove the excess charge on the transfer material while the guide member has the configuration like (1) and (2) (see Japanese Patent Application Laid-Open No. H10-048969 and Japanese Patent Application Laid-Open No. H10-250891).
However, in the conventional technology, all the problems (1), (2), and (3) can not be solved with the simple configuration.